This has nothing to do with changing the speed of sound. This changes the mix to speakers so each speaker gets its normal on time signal but it also feedbacks a cancellation signal to the specific speaker that is located where a bad reflection happens. This signal is filtered and delayed unrelated to the main signal. This is full spatial bass optimization, no summing in mono needed like we've been doing.
I will have to look into this more, but the fact remains that multiple speakers can only be timed to all give a single impulse transient at one location.
As far as reflections go, I can see how that could be ameliorated to an extent. But sound waves have vector, so no matter how much cancellation or other programs you choose, everyone in the room can not possibly get exactly the same balance of direct and reflected sound. What I do know is that the severe problems with issues of variability of sound from seat to seat are at their core caused by poor speaker performance. It is that old issue of variance of axis and off axis sound that is at the root cause of a good portion of this problem. My experience is that getting the direct and reflected sound to track closely is key here.
The other issue is that the speaker and the room are at best only 50% responsible. What I mean by this is that the recoding techniques have a huge part to play in this.
Poor microphone placement, selection and technique are a huge root cause of this problem.
This has really hit home to me this last couple of months. This is the Proms season and there have been daily or more concerts from the Royal Albert Hall since July 9 and continue until September 10. The sound, at least in my room has been incredible. All are on radio and online on iPlayer. Two each week are on TV. The BBC say they do separate mixes of the audio for TV and for audio only. Both have been superb, but the audio only stream a bit more expansive. For this year the BBC have gone back to the old Decca Tree above the conductors head, with minimal use of spot mics. I note this spot is often a mini Decca Tree. The Decca tree is central omni mic flanked by two Cardioid mics facing left and right, all about two feet or so apart. The bass is deep and natural just like the Decca recordings of years ago when they used this technique.
The point of all this is that the sound is very natural throughout the room. With the Dolby upmixer, imaging is incredibly good, not only left right but depth.
A few days ago I listened to Mahler No.2 (The Resurrection) under Sir Simon Rattle and the LSO with vocal soloists and two large choirs tiered either side of the organ, "The Voice of Jupiter".
The soloists were clearly in front, and realistically balanced. The orchestra and chorus stretched wide of the speakers, and the strings were in front, the brass and woodwind behind and percussion at the back. The choir were clearly behind the orchestra and and you could detect they were tiered way up higher than the orchestra. The sound stage was thrown way beyond the front wall of the room. The off stage trumpet, French horns and Flugel horns high up in distant high balconies were clearly reproduced and located. I think the ceiling speakers played a big part in this, and also giving that sense of the dome.
When the "Voice of Jupiter" added a huge foundation to the massive final chorus the effect was uncanny and complete.
So this convinces me that speakers, room and recording technique are the key to realistic spatial or immersion audio. This was incredibly close to the real live experience, with no boom or room affects upsetting the apple cart.
I have also been testing the new BPO Atmos immersive streams. They have not got this right at all yet. The bass does not seem right and for some odd reason the streams lack perspective and seem a bit top end heavy. The two channel stream with the Dolby upmixer is significantly more realistic with a better sense of space.
The BPO engineers need to go back to the drawing board on this.
I think we are only scratching the surface of the optimal mic techniques for Atmos concert hall recordings. I have read some research papers on mic techniques for Atmos concert hall recordings. There is no agreement. But a University study, from Sheffield, if I remember correctly, using blinded listening panels, showed a preference for a modified Decca tree mic arrangement, which I find interesting. I have to wonder if this is why, the BBC resurrected the old Decca tree for this years Proms.
My instinct is that room dimensions and treatment in the broadest sense to include furnishings carpeting, other décor, and perhaps judicious use of custom treatments as well as improved speakers coupled with better and more intelligently applied recording techniques will have the greatest impacts. Certainly my experience would suggest this is a very good and crucial foundation to progress to more realistic reproduction in the home.
I have no experience with Dirac, but for me Audyssey is a disaster and a major downgrade to quality and realism however employed. I regard that as a total dead end. However, I think properly used what we have currently at our disposal gets us a good deal of the way to hearing the recording environment imposed on out rooms, rather than the converse.
